In the 1960's the man at CBS Television who was responsible for editing films
to length for "The Late Show" told me that most films made before 1950 were so
tightly constructed that it was very hard for him to take out scenes without
upsetting the balance and the flow of plot information.  "But after 1950" he
said, "you can usually go in their and snip here and there and anywhere with
no problem!"
He went on to muse on the idea that as "movies" became appreciated more and
more as works of art their directors actually became more self-indulgent. They
weren't only "telling a story" any more, they were "putting themselves on the
screen."  That, my friend said, made it easy to cut!

Online resources for film/TV studies may be found at ScreenSite